1. Technical Field
The present invention relates to a communication processing device performing communication with a communication apparatus such as an Radio Frequency Identity (RFID).
2. Background Art
In related art, as the number of communication apparatuses increases at the time of performing communication with the communication apparatuses having identifying information such as an RFID tag, signals transmitted from the communication apparatuses collide with each other, whereby a communication processing device, for example, an RFID reader/writer which receives the signals from the communication apparatuses cannot normally receive the signals. A circumstance in which the signals collide with each other is called a collision. A process that prevents signals output by a plurality of communication apparatuses from colliding with each other so that the signals of a plurality of communication apparatuses can be read is called an anti-collision process.
The anti-collision process includes an anti-collision process employing a time slot, for example. More specifically, in the plurality of apparatuses having the identifying information arbitrarily allocated to any one of plurality of segments, which are called a time slot, time-dividing timing at which the signals are read and a random number is output to an apparatus included in one time slot for each time slot so as to perform division communication with the RFID tag. When the communication processing device can normally read the random number, it reads the identifying information from the communication apparatus outputting the random. When the plurality of communication apparatuses are allocated to the time slot and the random number output from the communication apparatus of the time slot cannot be read due to occurrence of the collision, the identifying information is not read from the time slot. Similarly, the random numbers are just output from the communication apparatuses of all the time slots. A period during the communication apparatuses are allocated to the time slots and the random numbers are output to all the time slots, and identifying information is read from a communication apparatus in which the collision does not occur is called a sequence. When one sequence is ended, a communication apparatus in which the information is not read is newly allocated to an arbitrary time slot and the above-mentioned process is carried out. The process is ended at the time when the sequence in which the collision does not occur is ended. By this configuration, it becomes possible to read the identifying information of the plurality of communication apparatuses.
In the anti-collision process (a slotted aloha method) employing the time slot described above, it becomes important to set the number of time slots so as to improve processing performance. For example, as the number of time slots increases, occurrence probability of the collision decreases. However as a result, since a process of whether or not to read the identifying information is performed for each time slot, a processing time within one sequence becomes increased. On the contrary, as the number of time slots decreases, the processing time within one sequence decreases. However, occurrence probability of the collision becomes increased.
Consequently, there has been proposed a technology of optimizing the number of time slots by slightly changing the number of time slots depending on the number of responses from the communication apparatus such as the RFID tag has bee proposed in the preceding sequence (for example, see Non-patent literature 1).
[Non-patent literature 1]
“EPC™ Radio-Frequency Identity protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960 MHz Version 1.0.9” [online], January, 2005, EPCglobal Inc™, [searched on Apr. 4, 2006], Internet <URL:http://www.epcglobalinc.org/standards_technology/EPC global2UHFRFIDProtocolVl09122005.Pdf> P. 84
However, in a conventional communication processing device, since the number of time slots is slightly changed depending on the number of responses in a preceding sequence without considering the number of communication apparatuses existing within an area in which the communication apparatuses can communicate with the communication processing device at the time of changing the number of time slots, it takes a long time to optimize the number of time slots depending on the number of communication apparatuses. Accordingly, there is a problem that it is difficult to sufficiently shorten a time required for an anti-collision process.
When the number of communication apparatuses which can communicate with the communication processing device is substantially turned out, the initial number of time slots may be set to a proper value depending on the number of communication apparatuses. However, it was difficult to acquire the number of communication apparatuses that can communicate with the communication processing device in the past.
Although the number of communication apparatuses was substantially turned out, it was difficult to determine what number of time slots is proper depending on the number of communication apparatuses. Accordingly, it was difficult to set the proper number of time slots.